hi everyone,
i am having interesting observations on reflowing AZ 40XT, the reflow suggested by the manufacturer (120C for 30 seconds) does not give a desired round surface profile. I have tried a protocol that is for AZ50XT (according to this: https://www.jove.com/video/55276/multi-step-variable-height-photolithography-for-valved-multilayer) overnight reflow with ramping of 10C/h up to 185C. This seemed too much and the features melted after such treatment.
I have also tried quicker ramping to 150C in 3 hours & keeping it at 150C for 20-30 mins, this generates a lot of bubbles and the features melt and since my features are very close to each other (34-30microns), they can fuse or be too close after reflow.
I have tried without ramping, straight going to 150 and 140 for 6 mins. After this, the features seemed to be round enough for my purpose, however the problem of random bubbles in the chip still exist.
Did anyone have such issues before? What might be the possible reasons for bubbles and how i could optimize to avoid them? and could you share your experience with reflow of exactly AZ40XT rather than 50XT?
i spin the AZ at 1600rmp for 40sec. I also coated the wafer with SU8 before putting AZ, seems much cleaner but the bubbles still persist. I rehydrated 1)overnight with a wet tissue 2) for 1 hour at 70C oven with wet tissues. Both are generating bubbles, method 1 less.
Thank you for any practical advice and suggestions. Possibly a suggestion on developed protocols for AZ40XT specifically since the manufacturer lacks them.
does anyone suggest using AZ50XT instead?
Thank you for your answer. Do you mean degassing the photoresist before spincoating?
I was going to suggest the same outgas step as Mr. Kundu. I've not used this exact resist, but have had similar issues with thick PMGI resists.
One solution is to let the sample sit for 5min or more BEFORE soft-bake (ie. right after spinning it). Apparently it allows some nitrogen etc. to diffuse out of the film. I don't remember the exact outgas time for PMGI, and your resist is much thicker, so maybe try a very long, eg. 60min, to see if it works before finding the minimum short time.
Also, the AZ40XT data sheet suggests a gradual three-step ramp up to the final bake temp, which probably helps as well. You could then try your reflow bake after that (or I guess you're combining the soft-bake and reflow into one step, which probably works too).
Hello Demis, thank you for your suggestion. Basically, the problem revolved around proper drying after rehydration and after development. I dried the wafer for 2-3 mins carefully with the air-gun and the problem completely resolved. Now, what could explain the bubbles appearing due to the lack of drying? does water tend to stay inside of the resist without drying which causes the bubbles after reflow?
Regarding the reflow, i tried several different procedures, and my structures are very close to each other. the best way was not to use the gradual ramping of the hotplate, but rather use the method of 3-2-1 glass slides on the final temperature on the hotplate, and then a more or less gradual cool down. this gave the best results for reflow so far at 142C. Which AZ data sheet are you referring to? Unfortunately, the reflow that is suggested on the AZ40XT data sheet doesn't occur in the same fashion. They suggest a much lower temperature for shorter time.
I have a feeling that AZ40xT tends to "boil" when subjected to higher temperatures. The solution in my case was a very long vacuum oven treatment (90 degrees overnight, but the longer the better). If there are gasses/solvent trapped in the resist, they will be released in this vacuum treatment and the resist will be able to be warmed-up to higher temperatures without boiling (or bubbling).
Hello, Mrs Alshanbayeva, Do you know where I can get the AZ 40XT-11D Thermal Flow data sheet? I have searched online for a long time but no result.
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